Modern disk arrays simultaneously operate a plurality of disk drives which are processed as a single disk unit through parallel combinations of units. This increases both performance and reliability are increased.
As a practical way to improve reliability, it has been recognized to provide an exclusive parity or hamming code disk within the disk array apparatus. Moreover, it is also known to provide a hot spare disk, so that even if a single disk develops a fault, processing can be done continuously without suspending the operation of the system.
In general, a plurality of magnetic disks are arranged in parallel within the disk array apparatus. Combinations of physical magnetic disks are grouped to form one or more logical disks. As to the combination method, several types have already been proposed. The respective types are called RAID (Redundant Array Of Inexpensive Disks) levels. For each RAID level, the control method of the disks combined as a logical disk is controlled by a different operation method.
The RAID levels are called RAID level 0 to RAID level 5. The concept of each RAID level and operating method are described in The RAID Book (The RAID Advisory Board, Inc. issued on Nov. 18, 1993).
Moreover, a disk array apparatus which allows coexistence of a plurality of types of logical disks within one drive module group has been developed. As seen in FIG. 1, a total of 24 disks, including six disks in the lateral direction and four disks in the vertical direction, are arranged in the matrix structure within one unit of the disk array apparatus.
In FIG. 1, the lateral arrangement of a drive module group 102 is called a rank. In general, one logical disk has a plurality of physical disks in the same rank.
The vertical arrangement is called a port. From the hardware point of view, data transfer may be realized independently for each port.
In FIG. 7A, an example of a logical disk assigning method is indicated. A device of rank(x)/port(y) is described as DVxy. The 24 devices are respectively assigned in such a manner that DV00-DV04 are defined as logical disk 0, while DV10-DV14 are logical disk 1, DV20-DV24 are logical disk 2 and DV30-DV34 are logical disk 3. HS-0, HS-1, HS-2 and HS-3 are assigned respectively as the hot spare disks. The hot spare disks are used to newly store data which was stored in a relevant physical disk when a fault is generated in the disk, disabling read and write operations of data in that disk. The data to be stored in the hot spare disks are reproduced from the contents of the other disks constituting a logical disk to which the relevant physical disks belong.
FIG. 7B shows the RAID level assigned to each logical disk in the structure explained above. In FIG. 7B, logical disks 0-3 are all set to RAID level 3 or RAID level 5.
FIG. 8A shows another example. In FIG. 8A, 24 devices are respectively assigned in such a manner that DV00-04 are defined as logical disk 0, DV10-DV11 as logical disk 1, DV12-DV13 as logical disk 2, DV14 as logical disk 3, DV20-DV22 as logical disk 4, DV23-DV24 as logical disk 5, DV30-31 as logical disk 6, and DV32-DV34 as logical disk 7. HS-0, HS-1, HS-2 and HS-3 are assigned respectively as hot spare disks. The function of the hot spare disks is similar to those of FIG. 7.
FIG. 8B shows the RAID level assigned to each logical disk in the structure described above. In FIG. 8B, the logical disk 0 is set to the RAID level 3 or 5, logical disks 1 and 2 to the RAID level 1, logical disk 3 and 4 to the RAID level 0, logical disks 5 and 6 to RAID level 1 and logical disk 7 to RAID level 0.
In the disk array apparatus of the structure explained above, particularly in the apparatus as shown in FIG. 8, a variety of logical disks of various RAID levels coexist. When such a structure is employed, a disk array controller cannot control the logical disks if the disk array apparatus does not accurately detect the layout of the logical disks. For example, in FIG. 8, DV10 to DV14 cannot be operated under the assumption that they are set to RAID level 3.
In order to prevent such an erroneous assumption, the position in the relevant drive module group for insertion of the relevant physical disk (referred to as "physical address") is recorded in each physical disk in the apparatus. Such information is generally known as AIR (Array Integrity Record) information. This AIR information is written in the factory before delivery.
The disk array apparatus inspects the physical address with reference to the AIR information recorded in the physical disk loaded therein. If mismatching between the actual inserting position and the physical address of the AIR information is detected, the relevant logical disk is disabled.
As explained above, erroneous recognition of logical disks resulting from erroneous insertion of a physical disk into an incorrect slot can be prevented. However, disk array apparatus developed in recent years is capable of providing a plurality of logical disks within one drive module group. In the disk array apparatus of the related art, an individual disk apparatus can be controlled on the basis of its physical position. Therefore, control of the logical disk also naturally depends on the physical position of the disks being correct. Accordingly, transposition or rearrangement of the logical disk within the apparatus has not been possible.